Flow batteries are electrochemical energy storage systems in which electrochemical reactants, typically redox active compounds, are dissolved in liquid electrolytes, which are individually contained in negative electrolyte or negolyte and positive electrolyte or posolyte loops and circulated through reaction cells, where electrical energy is either converted to or extracted from chemical potential energy in the reactants by way of reduction and oxidation reactions. Optimal performance of the flow battery relies on the ability to maintain balance between the posolyte and negolyte, both in terms of pH and state of charge. Upon extended cycling, flow batteries typically develop an imbalance in both proton and electron content between the posolyte and negolyte due to the presence of parasitic electrochemical side reactions. One reaction is the evolution of hydrogen gas from water at the negative electrode, which results in an imbalance in both the electron (state-of-charge) and proton content between the posolyte and negolyte. This imbalance, if left uncorrected, subsequently results in a decrease in system performance. An imbalanced state may be corrected by processing either the posolyte, negolyte, or both in a balancing cell.
Various methods have been described for balancing flow battery electrolytes. These methods primarily address balancing the electron (state-of-charge) content between the posolyte and negolyte. No methods have been described that adequately address the simultaneous balancing of both the electron and proton contents of these electrolytes The present invention is aimed at addressing at least this deficiency.